Riordan is a surname of Irish origin (Irish: Ó Ríordáin; Old Irish: Ó Ríoghbhardáin); Rearden is a variant of it. . From ri “king” and bard “poet”, it means “royal poet”. In Irish tradition, the poet was very highly regarded in any royal household, as he acted as scholar, historian and advisor to the king. People with the name. Ann Fienup-Riordan (born 1948), American cultural anthropologist. Bill Riordan (1908–1973), Australian politician from Queensland; minister for the navy 1946–1949. Daniel J. Riordan (1870–1923), American politician from New York; U.S. representative 1899–1923.
https://en.wikipedia.org/wiki/Riordan